Chambers for blood sets are commonly used in most or all blood sets for the prime purpose of removing gas bubbles from the blood. Such gas bubbles can interfere with the operation of dialyzers, and can be injurious to a patient if allowed to return to the arteriovenous system of the patient.
Conventional bubble traps comprise a typically rigid or semi-rigid tube in which a blood inlet is provided to convey blood into the top of the chamber, while a blood outlet draws blood from the bottom of the chamber. Bubbles are thus given the opportunity to rise to the top of the chamber so that the blood in the bottom of the chamber, which is withdrawn to pass through another portion of the blood set, is relatively free of bubbles, since they migrate to the top of the chamber.
See also Utterberg U.S. Pat. Nos. 5,328,461 and 5,520,640 as other examples of bubble traps for blood lines known to the prior art.
Typically, such bubble traps are taller than they are wide, to provide a deep, vertical chamber for the blood so that bubbles are kept away from the bottom of the chamber from which the blood is being withdrawn.
The inlets of the prior art bubble chambers are variably positioned, the idea being that the blood entering into such inlets, and the bubbles contained in the blood, will initially stay in an upper portion of the chamber so that the bubbles have time to migrate upwardly through a liquid level to a gas space at the top of the chamber. Some inlets are vertically oriented, extending downwardly from the top of the chamber. Because of the height of the chamber, inflowing blood stops moving downwardly before the bubbles contained in it can be caught in the outlet flow. Other inlets of the prior art are vertically oriented in the bottom of the chamber, to propel the inlet blood upwardly toward the chamber top. Other inlets are horizontally oriented in the side of the chamber, so that the inlet flow must horizontally cross the downward flow of the bulk blood in the chamber, moving to an opposite sidewall where it is turned upwardly. This raises the possibility of bubbles being entrained in the downward flow before they are turned upwardly to reach the intended air space.
The bubble trapping principles of the prior art are effective with large, buoyant bubbles, typically having a volume greater than 50 microliters, and at relatively low flow rates of less than 300 ml. per minute. Blood chambers for trapping bubbles typically have volumes of about 15-25 ml. The buoyancy of the bubbles typically urges them to the surface at a velocity greater than the downward velocity of the bulk flow of the fluid in the bubble trap.
However, such bubble traps are increasingly ineffective as bubbles get smaller, and/or as flow rates increase. Modern dialysis techniques often require blood flow rates exceeding 450 ml. per minute, which raises the risk that bubbles can get through bubble traps of the prior art.
To accommodate such higher flows, the volumes of some designs of prior art bubble traps have been increased. However, this is distinctly undesirable, since that increases the priming volume of the set. It is highly desirable to keep the priming volume of any blood set low, since it is important to minimize the amount of blood removed from a patient at any one time during a blood treatment procedure such as dialysis.
In a previous patent application by the applicants, wide bubble traps are disclosed in which the width of the bubble trapping chamber is preferably wider than the height of the chamber. The fluid inlet and fluid outlet to these chambers are then laterally spaced from each other to provide a fluid flow pattern which is substantially horizontal in nature, with less of a vertical flow component than in the prior art. This has been found to facilitate the migration of bubbles upwardly to the top of the chamber.
In other work by the applicants of this application, a bubble trap chamber, specifically shown to be cylindrical, contains a central inlet/outlet tube which serves as the inlet from one end and the outlet from the other end, having side apertures and a partition between the apertures to block direct flow between the inlet portion and the outlet portion of the tube.
However, there remains a need for a bubble trap which can be carried by a large variety of different dialysis machines, to greatly reduce the designs of blood sets that a manufacturer must produce and retain in inventory. Such a flow-through bubble trap is provided by this invention, while exhibiting the many advantages of substantially horizontal flow circulation in the chamber of the bubble trap. Substantial cost savings can be achieved, because the particular design of this invention can be used with a large variety of dialysis machines made by different manufacturers, to greatly reduce the numbers of designs that must be manufactured in order to keep a complete inventory. Also, the bubble traps of this invention can be directly connected to pump tubing to achieve further economies in the field of reduction of the amount of tubing material necessary to manufacture sets in accordance with this invention.